Measuring blood pressure information of a subject is extremely important in gaining an understanding of the state of health of the subject. In recent years, attempts have been made to determine the cardiac stress or the level of arteriosclerosis not only by measuring a systolic blood pressure value and a diastolic blood pressure value, the usefulness of which as typical indices that contribute to analysis of the risk of cardiovascular diseases such as stroke, heart failure, myocardial infarction, and the like has been widely acknowledged, but also, for example, by measuring the pulse wave of the subject.
Blood pressure information measurement devices are devices for measuring blood pressure information, and are expected to be further used in fields such as early detection, prevention, and treatment of circulatory diseases. It should be noted that the blood pressure information includes a wide variety of types of circulatory information, such as systolic blood pressure values, diastolic blood pressure values, average blood pressure values, the pulse wave, the pulse, various indices indicating the level of arteriosclerosis, and the like.
Generally, a cuff for a blood pressure information measurement device (hereinafter also simply referred to as “cuff”) is used to measure blood pressure information. Here, “cuff” means a band- or ring-shaped structure that contains a fluid bladder with an inner cavity and that can be attached to a part of a living body, and refers to those for use in measurement of blood pressure information, where an artery is compressed by inflating the fluid bladder by injecting a fluid, such as a gas, a liquid, or the like, into the aforementioned inner cavity.
Usually, a blood pressure information measurement device is provided with a pressurization pump and a discharge valve, which serve as a pressurization/depressurization mechanism for increasing/reducing the internal pressure of the fluid bladder. Of these two components, the discharge valve is intended to maintain the internal pressure of the fluid bladder in a closed state in which the discharge valve is closed, the internal pressure having been increased by the pressurization pump, and to reduce the internal pressure in an opened state in which the discharge valve is opened. A flow rate control valve, the operation of which is controlled when reducing the internal pressure of the fluid bladder and which thus can variably control the discharge flow rate, is preferably used as the discharge valve.
Conventionally, as disclosed in, for example, JP 6-47007A (Patent Literature 1), JP 6-47008A (Patent Literature 2), JP 2002-5330A (Patent Literature 3), and the like, solenoid valves whose valve bodies are electromagnetically driven have been commonly used as the flow rate control valve serving as the discharge valve.
Here, a solenoid valve includes a housing, a drive shaft with a valve body attached to an end, a permanent magnet provided in either the housing or the drive shaft, and an electromagnetic coil provided in the other of the housing and the drive shaft, and is configured so that the drive shaft can be moved in an axial direction by means of an electromagnetic force, which is generated in the electromagnetic coil by supplying current to the electromagnetic coil, and a repulsive force, which is then generated in the permanent magnet.
In each of the blood pressure information measurement devices disclosed in JP 6-47007A, JP 6-47008A, and JP 2002-5330A above, the solenoid valve is disposed opposite to a discharge port of the fluid bladder contained in the cuff, the valve body attached to the end of the drive shaft is configured so as to be able to close and open the discharge port as it moves, and thus the flow rate of the fluid discharged from the fluid bladder can be variably controlled.